Automotive vehicle speed control system

ABSTRACT

To improve the reliability of systems which, upon operation of the brake, must be disconnected but otherwise operate reliably, and to reduce the number of components required, a memory and control circuit is provided which includes an amplifier having a self-holding feedback connection. Upon receiving a &#34;disconnect&#34; signal, for example due to operation of the brake of the vehicle, control operation of the circuit is inhibited; upon operation of a &#34;resume&#34; switch, connected to the feedback junction, the self-holding feature of the amplifier in the &#34;disconnect&#34; mode is inhibited so that the circuit can again resume its control function.

CROSS REFERENCE TO RELATED APPLICATION

U.S. Ser. No. 705,923, filed July 16, 1976 Scheyhing et al, assigned tothe assignee of the present application.

The present invention relates to a control system for automotivevehicles to maintain the speed of the vehicle at a predetermined level,and having a disconnect memory which can be set in a disconnect mode bypredetermined disconnect signals and can be reset into a "resume" or SETmode by a "resume" signal.

BACKGROUND AND PRIOR ART

Automotive vehicle speed control systems must be capable of beingimmediately interrupted under certain operating conditions, for exampleupon operation of the brake, so that the speed control system does nottend to accelerate a vehicle if the operator wishes it to be slowed.Further, the system should not permit control of vehicle speed from astopped or low-speed operating condition of the vehicle. Thus, thecontrol system should be disabled below certain vehicle speeds. If thevehicle in which the control system is installed has a manually operatedtransmission, the control system should be disabled in the gear changeinterval to prevent excessive acceleration of the engine of the vehicle.Of course, it should also be possible to provide a manual disconnectswitch.

The various conditions above referred to provide disconnect signals. Adisconnect memory is provided so that, when one of the disconnectsignals is effective, the control system will not be inadvertentlyenabled even by operation of a manual connecting switch.

The system should, additionally, be capable of interconnection with theremainder of the vehicle system, for example with the brake lightswitch, so that the system will be disabled if the brake light switchshould become defective. Thus, if the actual vehicle speed differs fromthe commanded vehicle speed by a predetermined difference, control ofthe speed of the vehicle by the system should be inhibited. This lastcondition should, however, be capable of being overridden by a manuallyoperated control switch, for example by a "resume" switch so that, afterbraking of the vehicle, the actually commanded speed can be reachedautomatically by the speed control system.

Control systems have previously been proposed in which the disconnectmemory includes a relay having a switching contact connected in thecurrent supply circuit of the positioning element for the engine, andwhich controls, for example, fuel supply thereto. The relay itself iscontrolled by the respective collector-emitter paths of varioustransistors, which in turn are controlled over appropriate thresholdswitches to which the various disconnect signals are applied. Uponconduction of the transistors, operation of the ON switch can energizethe relay which is connected in a self-holding circuit for so long ascurrent supply of the control element for the engine is closed.Operating the relay as connected requires a substantial number ofcomponents, which is expensive in costs as well as in assembly. Due tothe relay, the system is subject to malfunction.

THE INVENTION

It is an object of the present invention to provide a vehicle speedcontrol system having a disconnect memory which is so arranged that thenumber of components is reduced, while being reliable in operation andparticularly meeting all safety requirements.

Briefly, the disconnect memory includes an amplifier which has aself-holding feedback circuit therein, the feedback circuit beingcontrolled by the "resume" signal from a manually operable "resume"switch.

This system permits elimination of mechanically movable components, thusdecreasing malfunction and increasing overall reliability. Due to thepossibility of constructing the entire system or at least a substantialportion thereof as an integrated circuit, the space requirements for thestructure are substantially reduced.

The control system can operate in analog, digital or hybrid form. If thecontrol system uses disconnect signals which are present in analog form,then suitable threshold switches can be used to convert them intodigital signals. These digital signals can then be applied to the inputand/or the output of the amplifier in order to control the disconnectmemory to change to blocking condition. In accordance with anadvantageous feature of the invention, the number of components of thesystem can be additionally reduced and one threshold switch can be savedif the amplifier is constructed to be a difference amplifier, having areference voltage applied to one terminal, the other terminal having ananalog-type disconnect signal applied. The amplifier will then not onlyoperate as an amplifier but additionally take over the function of acomparator and further that of a memory. In accordance with a preferredembodiment, a signal corresponding to actual speed is applied to theamplifier in analog form, and the reference voltage is so selected thatthe amplifier automatically changes to a "disconnect" state below acertain speed, for example about 25 km/h (about 15 mph).

The disconnect signal which is generated as a function of the differencebetween actual vehicle speed and commanded vehicle speed is applied tothe amplifier in dynamic form. This is a particularly advantageousembodiment of the invention since, if the disconnect signal hascontrolled the memory to change to its blocking or disconnect mode, itcan be reset to its "connect" or ON mode by manual operation of the"resume" switch, even if the actual speed is still less than thecommanded or desired speed. Thus, under certain conditions, it ispossible to permit the "resume" signal to supplant the disconnectsignal.

Drawing, illustrating an example: the signal FIGURE is schematic diagramof the system.

An actual speed signal generator 10 provides a d-c signal at its output11 which has an amplitude representative of vehicle speed. This speedsignal is applied to a controller 13, operating as a comparator. Thecontroller 13, for example an operational amplifier, additionally has acommanded speed signal applied thereto taken off the tap point of apotentiometer 12. The difference between command signal frompotentiometer 12 and the actual speed signal from terminal 11 of speedsignal generator 10 provides a positioning or error signal forpositioning element 14. The positioning element includes atransistorized power stage 15 to control a magnetic valve 16 which isoperatively connected to the throttle of the engine of the vehicle,together shown schematically by block 17.

The control system itself is shown only rudimentally and in generalprinciple. Further details are disclosed in the cross-referenceapplication Ser. No. 705,923, filed July 16, 1976, Scheyhing et al.

A disconnect memory and control circuit 20 includes the components toprovide the disconnect signal, as well as the components which process a"resume" signal.

Various disconnect signals can be applied to the memory and controlcircuit 20. A first disconnect signal is taken off the output 18 ofcontroller 13. This is an anolog disconnect signal and proportional tothe difference between actual vehicle speed and commanded speed. Thissignal is applied to a threshold switch 21, at the output of which anegative voltage is provided if the actual speed of the vehicle is lessthan the commanded speed by a certain predetermined value. The outputsignal of threshold switch 21 is conducted over capacitor 22 and adecoupling diode 23 to a junction 24, which may be termed the OFFjunction, to which disconnect signals are to be applied, junction 24being connected to the memory and control circuit 20. An additionaldisconnect signal is derived from output 11 of speed signal generator 10which is connected directly over a decoupling resistor 25 to the OFFjunction 24 to provide a signal thereto if the speed of the vehicle isbelow a predetermined value.

A manual OFF switch 26 is connected to control a transistor 27 to becomeconductive so that, if closed, the conduction of transistor 27 will alsodrop the voltage level at junction 24 to approximately negative orground level. The brake light switch 28 also provides a disconnectsignal. If the brake light switch 28 or a connecting switch 29 areoperated, a disconnect signal is provided. The coupling switch 29 isconnected through a resistor 30 which has a value substantially higherthan the resistance of the brake light (or brake lights, togetherrepresented by a single light) 31, so that, when the connecting switch29 is closed but the brake light switch 28 is open, the base oftransistor 27 is placed, approximately, at ground or chassis potential.If the connecting switch 29 remains closed but the brake light switch 28is closed or if the connecting switch is opened, a positive voltage willbe applied to the base of the transistor 27 so that it will becomeconductive and junction 24, effectively, will be placed at ground orchassis potential.

In summary: Operation of switches 26, 28, 29 provides positive voltagejumps which form disconnect signals which are inverted by the transistor27 to form negative voltage pulses at the junction 24 to serve asdisconnect signals. Negative voltage pulses to junction 24 areadditionally directly applied under conditions: low vehicle speed,through resistor 25, or excessive difference between actual vehiclespeed and commanded vehicle speed.

The memory and control circuit 20 includes a differential amplifierconstructed as an operational amplifier 40 having inverting input 41 anddirect input 42, and an output 43. Inverting input 41 of operationalamplifier 40 is connected to the tap point of a voltage divider formedof resistors 44, 45. Switching diode 47 and resistor 46 form a feedbackself-holding circuit. Switching diode 47 is so arranged in the feedbackcircuit that it is blocked if the "resume" switch 49 is closed to applya positive pulse through diode 48 to the feedback circuit. Diodes 48 and47 are reversely poled with respect to their common junctions.

Diode 50, connected to the output 43 of operational amplifier 40 blocksthe power or end stage 15 if the output 43 of the operational amplifieris, effectively, at ground or chassis potential since the diode 50 isthen conductive. If, however, the amplifier 40 switches over so that itsoutput has approximately the voltage of the power supply 51 --shown as abattery -- diode 50 will block and the power stage 15 can function ascommanded by the output of comparator amplifier 13.

Operation: A negative voltage pulse at the OFF junction 24 causes acorresponding voltage drop at the direct input 42 of operationalamplifier 40. Operational amplifier 40 will thus change state, and theoutput 43 will switch practically instantly to about chassis potentialfrom an output level of about supply voltage, that is, in digitalterminology, from a 1-signal to a 0-signal. This output voltage is fedback through resistor 46 and diode 47 to the direct input 42 so that,even after the OFF junction 24 no longer has a negative pulse appearingthereat, the operational amplifier 40 of the memory and control circuit20 will remain in blocked condition, in which the output 43 iseffectively at chassis potential, thus inhibiting control of thetransistor 15. This affect is obtained by the positive feedback circuit43-46-47-42. Closing the "resume" switch 49 does not change thecondition of operational amplifier 40 if the OFF junction continues tohave a voltage thereon which is less than the voltage determined by thevoltage division ratio of the voltage divider formed by resistors 44,45, and applied to the inverting input 41 of the operational amplifier40. Due to the positive feedback, the operational amplifier 40 willcontinue to remain in its blocked state even if the OFF signal at OFFjunction 24 has disappeared. If at that time, however, the "resume"switch 49 is operated, a "resume" signal will be generated, applied overdiode 48 to inhibit self-holding of operational amplifier 40 byinterrupting its feedback signal, and resetting operational amplifier 40to provide its "high" output and hence the memory and control circuit 20in its normal condition. The output 43 of the operational amplifier 40will then again switch to almost supply voltage, so that diode 50 willblock, and the power stage 15 can continue to control the valve actuator16. Disconnect signals which occur only briefly may, for example, begenerated by the brake light switch 28 when the brake is momentarilyopened for temporary speed reduction; or, for example, during manualgear changes as sensed by the circuit, for example, by opening ofconnecting switch 29 or, for example, upon increase in speed of thevehicle beyond the minimum speed after having reached, for example, adowngrade.

The control system is characterized by the particularly simpleconstruction of the memory and disconnect switch, which does not userelays which are subject to malfunction. The output 11 of the commandspeed signal generator 10 may, of course, also be connected over athreshold switch to provide a digital output signal which is thenapplied in digital form to the OFF junction 24. This increase incomponents can easily be avoided, however, if the reference voltage asapplied by resistors 44, 45 to the operational amplifier is so selectedthat the operational amplifier additionally acts as a comparator withrespect to the analog voltage of the OFF junction 24 and changes intoits blocked condition if the analog signal applied from speed signalgenerator 10 to the OFF junction 24 through resistor 25 drops below thevoltage applied to the inverting input 41 of the operational amplifier.Applying a disconnect signal to the OFF junction dynamically overcapacitor 22 ensures that the differential speed OFF command can besupplanted by a "resume" signal, as desired in the usual operation ofautomotive vehicles.

Various changes and modifications may be made; for example, thedisconnect signals applied to the OFF junction 24 could also be appliedto the output 43 of the operational amplifier since resistor 46 anddiode 47 feed back to the direct input approximately the voltage at theoutput 43 thereof.

We claim:
 1. Vehicle speed control system comprising means (13) togenerate a speed command signal;control means (14, 15, 16) to controlthe engine of the vehicle in accordance with a speed control outputsignal; a disconnect signal memory and control circuit (20) connected tocontrol application of the speed control signal to the control means(114, 15, 16) and including an electronic amplifier (40) having aself-holding feedback connection (46, 47), an OFF junction (24)connected to the disconnect memory and control circuit (20) to set thecircuit to a disconnect mode generating a disconnect signal and inhibitapplication of the speed control signal to the control means (14, 15,16); and a "resume" signal generating switch (49) connected to the selfholding feedback connection (46, 47) of the amplifier (40) to disableapplication of the feedback signal from the output (43) of the amplifierto its input (42) and reset the amplifier to permit transfer of thespeed control signal to the control means (14, 15, 16).
 2. Systemaccording to claim 1, wherein the feedback circuit comprises a seriesconnection including a resistor (46) and a switching diode (47);and theresume switch (49) is connected to apply a signal to the switching diode(47) to block conduction thereof upon operation of the "resume" switchto disable the memory and control circuit (20).
 3. System according toclaim 1, wherein the OFF junction (24) has digital type signals appliedthereto, said signals being connected to the amplifier (40) to affectits signal transfer.
 4. System according to claim 3, wherein theconnection between the OFF junction (24) and the amplifier (40) isdirectly to an input (42) of the amplifier (40).
 5. System according toclaim 3, wherein the connection from the OFF junction (24) to theamplifier (40) is through said feedback connection (46, 47).
 6. Systemaccording to claim 1, wherein the amplifier comprises a differentialamplifier, one input being connected to have the signals applied to theOFF junction (24) connected thereto, the other input being connected toa reference voltage;and wherein one of said inputs comprises an analogvalue representative of an operating condition of the vehicle.
 7. Systemaccording to claim 1, further comprising means (21) providing a"disconnect" signal to said OFF junction (24) when the differencebetween actual vehicle speed and commanded vehicle speed exceeds apredetermined value;and a capacitor (22) connected between saiddifference generating means (21) and said OFF junction (24) to effectdynamic application of the disconnect signal representative of saiddifference to the OFF junction and permit supplanting of the disconnectsignal from the memory and control circuit upon operation of the resumeswitch (49) even though the difference between actual and commandedspeed above said predetermined value continues to persist.
 8. Systemaccording to claim 1, further comprising switch means (26, 28, 29; 21,22) applying digital OFF command signals to the OFF junction (24);speedsignal generating means (10) providing an analog speed signal to saidOFF junction (24); said amplifier (40) comprising an operationalamplifier connected as a differential amplifier having one input thereofconnected to a reference voltage, the other input being connected tosaid OFF junction having said digital type and said analog signalsapplied thereto, said operational amplifier responding to the digitaltype signals by suddenly changing its output at its output terminal (43)between two levels, and further suddenly changing its output ifcomparison of said analog signal with said reference drops below thereference level, to provide for the disconnect signal if the speedsignal has dropped below a level representative of speed of the vehicleat which said system should not control vehicle operation.